Processing apparatus for use in diffusion transfer copying

ABSTRACT

A processing apparatus for quickly obtaining, according to the silver complex diffusion transfer process, radiographic images of surgical interventions. The apparatus comprises separately driven pairs of inlet rollers for introducing an image-receiving sheet and a radiation-sensitive sheet in the processing liquid. The image-receiving sheet follows the upper path in the processing liquid and leads the radiation-sensitive sheet which follows the lower path. Edge guides which are curved in the longitudinal direction and which converge towards each other in the transport direction of the sheets support the sheets in the processing liquid. A longitudinally curved guide plate is provided under the lower sheet path and has a plurality of openings through which processing liquid is pumped so as to cushion the sheet which follows said lower path. The driving of the inlet roller pairs is accomplished through control apparatus which creates a relative delay in the advance thereby of the image-receiving sheet in order that the leading edge of the radiation sensitive sheet may trail the same by a short distance.

United States Patent Stievenart [s4] PROCESSING APPARATUS FOR USEIN DIFFUSION TRANSFER COPYING [72]' Inventor: Emile Frans Stieveuart, Hoboken Bel um... [73] Assignee: Gevaert-AGFA N.V., Mortsel,

1 Belgium [22] Filed: July 6, 1970 [21] Appl. No.: 52,375

[30] Foreign Application Priority Data July 7, 1969 Great Britain ..34,203/69 [52] US. Cl. ..95/89 L, 355/100, 355/106, 95/89 R, 95/89 A, 95/89 F [51] Int. Cl. ..G03d 3/00 [58] Field of Search..........95/89 L; 355/10, 100, 106

[56] References Cited UNITED STATES PATENTS 3,092,005 6/1963 Limberger. ..95l89 L 3,017,816 1/1962 Stuckens ..95/89 L 3,435,750 4/1969 Limberger ..9 5/89 X 2,732,778 ll 1956 Limberger ..95/89 L FOREIGN PATENTS 0R APPLICATIONS 377,648 6/1964 Switzerland ..95/89 L 405,930 7/1966 Switzerland ..95/89 L Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard M. Sheer Attorney-William J. Daniel [57] ABSTRACT A processing apparatus for quickly obtaining, according to the-silver complex diffusion transfer process,

, radiographic images of surgical interventions. The apparatus comprises separately driven pairs of inlet rollers for introducing an image-receiving sheet and a 1 radiation-sensitive sheet in the processing liquid. The

image-receiving sheet follows the upper path in the processing liquid and leads the radiation-sensitive sheet which follows the lower path. Edge guides which are curved in the longitudinal direction and which converge towards each other in the transport direction of' the sheets support the sheets in the processing liquid. A longitudinally curved guide plate is provided under the lower sheet path and has a plurality of openings through which processing liquid is pumpedso as to cushion the sheet which follows said lower path. The driving of the inlet roller pairs is' accomplished through control apparatus which creates a relative delay in the advance thereby of the imagereceiving sheet in order that the leading edge of the radiation sensitive sheet may trail the same by a short distance.

ZCIaimsADrawingfiures PROCESSING APPARATUS FOR USE IN DIFFUSION TRANSFER COPYING The present invention relates to processing apparatus for use in producing images according to the silver complex diffusion transfer process.

In the performance of the silver complex diffusion transfer process an image-wise exposed radiationsensitive sheet, hereinafter called the radiation-sensitive sheet, is treated with a processing liquid to bring about development of the latent image and is pressed against a sheet material, hereinafter called the receiving sheet, to which complexed silver halidev diffuses from the radiation-sensitive material and is transformed to form a positive image of the object to be reproduced.

In practice the sheets. are made to follow separate paths one above the other, through a body of processing liquid, and as they emerge from the processing liquid they are pressed together by a pair of pressure rollers. The separate paths for the sheets in the processing liquid are usually determined by curved guide plates.

Apparatus of the described kind of work satisfactorily when used for the processing of low to medium speed photographic materials wherein black and white line images are to be produced.

When, however, such apparatus are used for the processing of high sensitive photographic materials wherein a continuous tone image is to be formed, difficulties are caused by the uncontrolled contact of the silver halide emulsion layer of the radiation-sensitive sheet with portions of the adjacent guide plate, thus leading to a locally increased development of the radiation-sensitive layer as a result of which the image density on the receiving sheet is correspondingly affected.

The mentioned difficulty is particularly observed when a continuous tone imageof an object exposed to X-ray radiation is produced according to the silver complex diffusion transfer process. This technique has been particularly developed for quickly obtaining radiographic images of orthopedic surgical interventions, and it will be understood that in this application the discernability of each detail is of paramount importance so that defects as mentioned hereinbefore are intolerable. A

Known apparatus wherein the separate paths for the sheets through the processing liquid are determined by longitudinally curved edge guides, i.e., guides which are curved in the direction of travel of thesheets and which make frictional contact with the opposed margins of the sheet which are parallel with the direction of travel, do not always lead to satisfactory results, especially in the case of large size sheets as used in radiographic work as hereinbefore mentioned. This is because the sheets may be so flexible that their flexure in the longitudinal direction is insufficient to prevent any flexure of the sheets under their own weight in the transverse direction. Whereas the longitudinal flexure may pre'vent such transverse flexure as would cause the sheet margins to retract out of the edge guides, such longitudinal flexure may not prevent substantial flexure of the leading and the trailing portions of the sheets. In consequence, the leading and trailing portions of the sheet following the upper path may make premature uncontrolled contact with the lower sheet and thus lead to impairment of the image quality.

Whereas such undesirable mutual contact of the sheets may be avoided during the first part of their travel by widely spaced edge guides, the said contact is difficult to avoid where the sheets approach the outlet pressure roller pair, because the sheet paths determined by the edge guides necessarily converge towards each other and the said edge guides terminate some distance before the nip of said pair of pressure rollers.

The present inventions aim at providing an improved apparatus for use in the production of images according to the silver complex diffusion transfer process.

The processing apparatus accordingto the invention comprises: A

' a. a tray for holding a body of processing liquid, wherein edge guide means are provided which determine for a radiation-sensitive sheet and for a receiving sheet two separate and vertically spaced paths through the tray, which are curved in the longitudinal direction and which converge towards each other from the inlet to the outlet of the tray,

b. pairs of inlet rollers at the inlet of the tray for driving said sheets separately towards said edge guide means,

c. a pair of outlet rollers provided at the outlet of the tray for pressing the two sheets together and for removing them from the tray, g

d. control means controlling the operation of at least one of said inlet rollers so that the sheet which follows the uppermost path leads the lower sheet over at least a few centimeters during at least the second half of the path of the sheets through the tray.

Although it is theoretically indifferent which of the two paths is followed by any of the two sheets, when the apparatus is used, the radiation-sensitive sheet preferably follows the lower path because otherwise its leading portion does not take part in the diffusion transfer and part of the image is lost. In case said radiation-sensitive sheet follows the lower path indeed, the length of the receiving sheet must equal at least the length of the radiation-sensitive sheet plus the length of the leading portion, because otherwise also part of the image is lost. Preferably, however, the receiving sheet is even slightly longer so that its trailing edge extends over the corresponding edge of the radiation-sensitive sheet. The reason therefore will be further explained in the description. 1

The sheets to be processed in the apparatus according to the invention may be square or rectangular and in the case of rectangular sheets their shorter or their longer side may be in the transport direction provided the size of the edge of the sheet which is leading cor-,

responds'with the transverse distance between the edge guides.

In case very flexible sheets must be treated, such as a radiation-sensitive material for radiographic recording which comprises a silver halide emulsion layer coated on a triacetate film support measuring 24 X 30 cm and having a thickness of 0.12 mm, difficulties may be encountered with the transport of the sheet which follows the lower path in the apparatus because the curvature of the lower path will usually be less than that of the upper path.

A curved guide plate may be provided under the lower sheet path in order to support the sheet which follows said path but in the case of highly sensitive materials, such as materials for radiographic recording as described above, even friction at the rearside of the radiation-sensitive material may cause a non-uniform processing.

According to a further preferred embodiment of the invention, means is provided which produces under the lower sheet path an upwardly directed liquid stream which cushions the sheet following said path at least over its central longitudinal area.

Such means may comprise a longitudinally curved guide plate which runs under the lower sheet path closely parallel thereto and which is provided near the lowest point with openings spaced apart in the transverse direction, and pump means for pumping processing liquid upwardly through said openings so that the streams of liquid through said openings cushion the sheet and flow upwardly towards the inlet and outlet of the tray.

An embodiment of the invention selected by way of example only will be described with reference to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic view of an apparatus according to the invention,

FIG. 2 is a plan view of the processing section of this apparatus, and

FIG. 3 is a diagrammatic cross sectional view of the processing section and inlet arrangements for the sheets;

FIG. 4 is the DC electrical circuit controlling the operation of the apparatus.

As may be seen in FIG. 1, the apparatus comprising a housing which has a hinged lid 11 which may be lifted for the introduction of an exposed film cassette into the apparatus, a narrow tapered chutel2 for the introduction of an image receiving sheet, and an outlet opening 13 through which both sheets upwardly leave the apparatus as they have been processed.

The housing 10 forms a light-tight enclosure for the apparatus, except for the chute l2 and the outlet opening 13. However, the innerfaces of the chute 12 are light-absorbing, e. g., by dull black painting, so that only light radiation entering axially of the chute can reach the processing station 15, whereas light which may enter'through the outlet opening 13 is sufficiently entrapped by the elements of the drying station, so that, even when the apparatus is used in daylight conditions, the light which may enter the apparatus is sufficiently weakened to not interfere with the proper operation of the apparatus.

Within the housing 10, a cassette unloading station 14, a wet processing station 15 and a drying station 16 are provided. Furthermore, the apparatus includes electrical supply means and roller driving means, not shown in the drawing.

The cassette unloading station 14 comprises a stationary sloping support plate 19 on which two laterally spaced parallel guides are provided. The sides of the two guides which face each other have a concave profile which is adapted to slidingly engage the laterally spaced cassette sides in order to accurately guide the cassette as it is slid downwardly over the support plate 19 until the leading edge of its frame abuts against arrest members of the guides, not shown. Each guide comprises an upper guide part 20 which is hinged to the support 19 at point 21, and a lower guide part 22 which forms an extension of the upper guide part and which is hinged thereto at point 23. The reason of this particular arrangement is as follows. From the introduction of the description it will be apparent that the apparatus according to the invention is suited in principle for treating only one sheet width, viz. the size which is determined by the lateral distance between the edge guides. It is possible, however, to treat two differently sized sheets in the apparatus, with a proviso that the size of the edge of the sheet which runs transversely of the apparatus corresponds with the distance between the edge guides. Thus, the present apparatus has been designed for the processing of 24 X 30 and 30 X 30 cm films the sheets. The film sheets being located in cassettes of the corresponding dimensions, in the case of 24 X 30 cm films the shorter sides of the cassette will lie alongside the lower guide parts 22 which, as the eassette is opened, will pivot on pivots 23 and thus take a position 24 as shown in broken lines, whereas in the case of 30 X 40 cm film sheets the longer sidesof the cassette will lie alongside the lower and the upper guide parts which, as the cassette is opened, will take a position 25.

The cassette opening mechanism is arranged for cooperation with X-ray cassettes, the cover of which is pivotally attached at one of its borders to a bottom flame by means of hinges, and which cassettes have a pin or the like pivotally attached on their cover, which pin has flat portions which may cooperate with a locking edge on the part of the cassette frame situated opposite the hinges. The tumable pin is provided with a tongue which is accessible at the outside of the cassette cover and which may be lifted in order to rotate the pin and unlock the cassette.

The cassette is located on the support plate 19 so that its cover is turned downwardly and its hinged margin is trailing.

The cassette opening mechanism comprises unlocking means (not shown) which is located under the support plate 19 and which may reach through an opening in the plate for gripping and pulling the cassette tongue so as to unlock the cassette. Additionally, the unlocking means also firmly holds the cassette cover pulled against the support plate when the cassette frame is lifted.

The cassette opening mechanism further comprises lifting levers 26 which are pivotally secured to the lower guide parts 22 and which may lift said parts after the unlocking of the cassette so that said guide parts, together with the cassette frame, may be brought into one of the two positions shown in broken lines.

The cassette unlocking and the cassette opening mechanisms are operated through a handle 27 which is provided at the outside of the apparatus, and which may be pivoted, and pushed and pulled, by the operator in order to operate the mechanism.

The processing station 15 is shown more in detail in FIGS. 2 and 3. It comprises a rectangular tray 30 wherein a concavely curved plate 31 is provided which is supported on a transversely extending vertical wall 32 and on a horizontal plate 33. Plates 31 and 33 fit to the innerside of walls 34, 35 and 40 of the tray so that the space under plates 31 and 33 does not communicate with the processing section of the station.

Two laterally spaced edge guides 36 and 37 are mounted on the curved plate 31, and they are formed by blocks of solidmaterial, which for the sake of clearness have been hatched in the drawing of FIG. 2, and

wherein grooves 38 and 39 have been provided which determine two separate paths for the sheets to be transported through the processing solution.

The processing'solution is pumped to the processing section through a conduit 41 which communicates with a semi-circular channel 42 which extends transversely at the lower side of the curved'plate 31. The channel 42 has closed lateral ends and it communicates through-a plurality of transversely spaced circular openings 43 withthe interior of the processing section.

The level of the processing solution in the tray is determined by an overflow system which is provided in a small cubical chamber 44 which is mounted against the outside of the wall 40 and which communicates with the interior of the tray over the support plate 33. The chamber has an upstanding overflowwall 45 which determines the level of the processing liquidin the tray, as indicated by'the dash and dot line 70, and an outlet conduit 46. Additionally, an outlet conduit 47 which communicates with the lowest point of the wet processing section is provided, the function of which will be explained further on in the description.

The inlet arrangement to the processing station is formed by a first pair of rotatable inlet rollers 48 for'introduction of the radiation-sensitive sheet, and by a second pair of rollers 49 for introduction of the receiving sheet in the processing tray.

The path which is followed bythe radiation-sensitive sheet as it slides downwardly out of the opened cassette towards the inlet arrangement, is indicated by the arrow 50 in FIG. 3. The sheet strikes with its leading edge'two laterally spaced flexible spring fingers 51 and the lower end portions of which intercept the free path of the sheet. Each of the spring fingersconsists of a length of spring wire, curved as shown inthe drawing, and welded at the upper side to upstanding fixed brackets 52. The flexibility of the fingers is such that they are capable of being put into vibration as they are struck by the'leading edge of the lowering sheet.

A sloping plate 53 forms a lower guide to the'nip of the inlet rollers 48, and its runs at an acute angle in respect of the support plate 19 which determines the direction of the path50 followed by the radiation-sensitive sheet. A microswitch 54 is mounted on a bracket below the plate'53, and its actuating lever 55 projects through a corresponding slot opening in the plate and intercepts the path followed by the sheet to the nip of the rollers.

The path of the receiving sheet is indicated by the arrow 56 and leadsthrough the chute '57 to the nip of the rollers 49. The receiving-sheet actuates the lever of a first microswitch 60 as it approachesto chute 57 and as the leading edge of the sheet reaches a few centimeters beyond the nip of the rollers 49, the'sheetactuates the lever of a second microswitch 61 which lever projects through a recess in the periphery of one of said rollers.

The sheetsare removed from the processing station by a pair of outlet pressure rollers 63' which are located so that the plane of contact between them, shown in the drawing by the dash and dot line 64, extends over the edge 82 of the plate 31. An idler roller 65 is mounted ahead of the outlet rollers 63 and prevents substantial deflection of the receiving sheet from its path towards the nip of the outlet rollers.

The drying station of the apparatus (FIG. 1 comprises a plurality of vertically spaced pairs of pressure rollers 66 between which pairs of guide plates 67 are provided. Heatingplates 68 and 69 are provided at opposite sides of the sheet path in the drier, and they may be uniformly heated by means of embedded electrical heating elements.

The rollers of the processing and of thedrying station have a resilient covering of butyl rubber or the like and they are directly coupled, exceptfor the roller pair 49, by conventional transmission means such as timing belts, chains and sprockets, etc., to a common driving motor so that they may be rotated at equal peripheral speeds.

The pair of inlet rollers 49 is coupledto said driving system througha magnetic clutch which is actuated by a solenoid 71 shown in the electric circuit of FIG. 4.

The A.C. part of the electric circuit of the apparatus comprises the driving motor (not shown), the circulation pump 72 for the processing liquid, the electromagnetic valve 73 (FIG. 1), the heating elements of the plates 68 and 69, a thermostatic heater 74 for the processing liquid, and a rectifier (not shown). The

rectifier provides the DC. supply of the electric circuit, shown in FIG. 4, which controls the automatic operation of the apparatus. The numerals of the contacts in said circuit correspond to the numerals of the microswitch in FIG. 3 and the contacts have been shown in the rest position of the apparatus. A time delay mechanism 75 is controlled by contact 54 and its output current is supplied via diode 76 to the solenoid 71 and indicated by a pilot lamp 77.

The operation of the apparatus is described hereinafter in connection with photographic materials which were prepared as follows.

For preparing the radiation-sensitive material, a high sensitive gelatino silver bromo-iodide (3 moles percent iodide) emulsion with a ratio of gelatin of silver nitrate of 1.5, was applied at one side of a gelatin-subbed cellulose triacetate support having a thickness of 0.1 mm in such a way, that per sq.m an amount of silver halide equivalent to 2.5 g of silver nitrate was present. After drying, an unhardened gelatin layer was applied to the light-sensitive emulsion layer in an amount of l g of gelatin per sq.m.

The image-receiving material was prepared by applying an image-receiving layer to agelatin-subbed cellulose triacetate support having a thickness of 0.1 mm. This image-receiving layer was applied in an amount of 1 litre per 10 sq.m from the following coating composition:

water 825 ccs gelatin 4! g 0.2% by weight dispersion of nickel sulphide nuclei in a l0% aqueous solution of gelatin 41 ccs 1% solution in ethanol of bis(dimethylthiocarbamoybsulphide 82 ccs 12.5% aqueous solution of saponine 4 ccs sodium thiosulphate-S-water 5 g 20% aqueous solution of formaldehyde 2 ccs A sheet of radiation-sensitive material measuring 30 by 40 cm was placed into a corresponding metal cassette adapted for co-operation withthe illustrated apparatus. The rear-side of the sheet was facing the hingeable cover of the cassette, and at the emulsion side of the sheet a usual calcium tungstate fluorescent screen was provided in the cassette.

The alkaline processing liquid contained in the tank 80 of the apparatus has the following composition:

distilled water 600 ccs l-phenyl-3-pyrazolidinone l g anhydrous sodium sulphite 75 g sodium hydroxide 7.8 g hydroquinone 16 g p-monomethylaminophenol sulphate g potassium bromide l g anhydrous sodium thiosulphate 50 g distilled water to 1000 ccs ethanol 200 cos 1% solution of 3-heptadecyl-4-mfluorosulphonyl phenyl-ureido-M- 1,2,4-triazoline-5-thione in ethylene glycol monoethyl ether 20 cos The pH of this processing liquid amounted to l 1.2.

The above described photographic materials and the processing liquid are described in French Pat. Specification No. 1,564,975 to which reference may be made for further details about a method and materials for producing radiographic images according to the silver complex diffusion transfer process.

The cassette containing the radiation-sensitive sheet is exposed to a skull phantom which is subjected to X- ray radiation produced by an X-ray tube located at 75 cm distance and fed by a tension of 75 KV and drawing of current of 64 mA.

The apparatus is started by closing the main switch so that the following actions taken place.

The pairs of rollers 48, 63, and 66 rotate continuously. The electromagnetic valve 73 is closed. The pump 72 draws processing liquid from the tank 80 and pumps it into the processing station 15. When the liquid has reached the level 70, it flows through conduit 46 back to the tank 80. The temperature of the processing liquid is controlled by the thermostatic heater 74.

The operator takes a receiving sheet measuring about 43.5 by 30 cm and he inserts the sheet into the chute 12, the shorter sheet side running transversely of the apparatus and the image-receiving side facing the cassette unloading station. The leading edge of the sheet actuates the microswitch 60, the corresponding contact is closed, and the solenoid 71 of the magnetic clutch is energized so that the pair of rollers 49 starts to rotate. The sheet is pulled downwardly by the rollers until its leading edge actuates the microswitch 61 whereby the corresponding contact is open, the solenoid of the magnetic clutch is de-energized, and the rollers come to arrest. The leading margin of the sheet has engaged in this position the edge guidemeans in the tray, but is not yet immersed in the processing liquid.

The operator now opens the cover 11 of the apparatus and slides the cassette containing the exposed film downwardly over the support 19, the longer cassette sides engaging the lateral guides 20 and 22. The cover 11 is closed and the apparatus is ready for operation.

The working cycle is started by manipulation of the lever 27 whereby the cassette is unlocked, and the cassette frame is lifted into the position 25. The radiationsensitive film sheet slides downwardly out of the opened cassette, it generally follows the direction indicated by the arrow 50 and abuts with its leading edge against the spring fingers 51 and the lever 55 of microswitch 54. It is without importance whether this abutment occurs simultaneously or successively. The spring fingers slightly deflect the sheet so as to guide it towards the nip of rotating roller 48. The light vibration of the fingers, as a consequence of the impact by the leading edge of the sheet, promotes the gentle lowering of the sheet and the aligning of its leading edge parallel to the nip of the rollers 48. v

The actuation of the microswitch 54causes the closing of the corresponding contact and starts thereby the delay device 75.

The delay device performs a complete working cycle within a time which depends on the size of the cassette, i.e., of the sheets, being treated, and which is independent of the opening or closing of contact 54 once the cycle has started. The delay device connects the D.C. line of the electric circuit to the lead 78 after few seconds and maintains this connection until the end of the cycle. This is done for the following reason.

If said connection were established directly by contact 54, the clutch controlling were established directly by contact 54, the clutch controlling the rotation of rollers 49 would be energized upon the actuation of the microswitch 54 so that the further advance of the receiving sheet by the rollers 49 would start even before radiation-sensitive sheet would have been gripped by the rollers 48. In that way, the receiving sheet would lead the radiation-sensitive sheet over two great a distance which would cause a loss of part of the image.

The driving of the rollers 49 is started therefore after the leading edge of the radiation-sensitive sheet has taken the position as indicated by the cross 79 (FIG. 3), so that the receiving sheet leads the other sheet over a distance of about 2.5 cm.

Both sheets are introduced into the processing liquid while following the paths determined by the grooves 38 and 39.

The path which is determined by the groove 39 is rather strongly curved so that the receiving sheet is sufficiently stiffened in the transverse direction to prevent substantial flexure of the sheet, except for the leading portion of the sheet which may tend to shown a more marked flexure. The path which is followed by the radiation-sensitive sheet is less curved and the sheet tends to rub over the plate 31. However, as the leading edge of the sheet passes over the openings 43, the upwardly directed liquid streams are deflected into streams which flow between the film surface and the surface of the plate 31 so that the film sheet is gently cushioned.

When the receiving sheet leaves the edge guides, its leading margin tends to follow a straight path until it slides along the upper part and the edge 82 of the guide plate whereby it is directed to the nip of the rollers 63. When said leading margin is gripped by the rollers 63, it tends to lie in the contact plane which is indicated by the dash and dot line 64 and which runs clear of guide plate 31. Thus, as the sheet is gripped by the rollers 63, it is kept free from the end portion of the plate 31 and from the edge 82, so that premature contact with the lower radiation-sensitive sheet is avoided.

When the radiation-sensitive sheet leaves the edge guides, the cushioning effect of the liquid gradually decreases because the liquid streams can escape laterally of the sheet at the zone comprised between the end of the guidesand the level of the liquid. However, the sheet is abundantly wetted at its'rear side so that it smoothly glides over the upper part of the plate 31 as it is directed hereby in a direction which converges towards the nip of the rollers 63. Since the radiationsensitive sheet is trailing in respect of the receiving sheet, it has not been contacted therebywhen the leading portion of the receiving sheet rubbed over the guide plate; The properdiffusion transferprocess only starts at the very moment when both sheets are intimately pressed into each other by the outlet rollers63.

The risk exists that during the transport of the trailing portions of the sheets through the processing station, also the trailing edge of the receiving sheet may flew excessively and thereby touch the lower located radiation-sensitive sheet. This risk is avoided if the trailing edge of the receiving sheet trails some distance behind the corresponding edge-of the radiation-sensitive sheet.

After the sheets have left the processing station 15, they remain in contact for some time untilthey enter the drying station 16. In the drying station the sheets are heated uniformly by the heating plates 68 and 69 and they are firmly pressed against each other in passing between the successive pairs of pressure rollers 66. Guide fingers 67 prevent the sheets from following diverging paths.

When the sheets leave the outlet opening 13 of the apparatus they separate from each other almost spontaneously, and the receiving sheet shows a positive X- ray copy which is sufficiently dry for examination purposes. The leading and the trailing margins of the receiving sheet are free from any part of the image and the operator can hold the sheet by these margins without harming the image.

An additional advantage of ensuring that the leading and trailing portions of the receiving sheet project from the corresponding edges of the radiation-sensitive sheet is that the emulsion side of the radiation-sensitive sheet is effectively screened from any contact with the outlet pressure rollers 63 so that no silver halide emulsion can deposit on the surface of the upper roller of the roller pair 63.

The adjustment of the delay device 75 is such that its cycle is completed when the sheets have left the processing station. The D.C. tension on line 78 of the electric circuit is removed so that the solenoid 71 is deenergized and the rollers 49 stop, and the pilot lamp 77 is extinguished. The operator knows that the apparatus is now ready for a next operation, and he does not need to wait until the sheets which are in the drying station have left the apparatus.

The following data relate to a particular embodiment of the apparatus which has just been described, and of its use:

Sheet-size (radiation-sensitive sheet): 24 X 30 cm and 40 X 30 cm Sheet-size (receiving sheet): 27.7 X 30 cm and 43.5

X 30 cm Processing time for greater sheet size: 1 sec.

Processing time for smaller sheet size: 95 sec.

Access time for greater sheet size: 70 sec.

"be transported without risk of the liquid flowing over the tray walls.

The following modifications may made to the apparatus.

The cassette unloading station may be arranged for cooperation with other types of cassettes than the type described. The receiving material need not necessarily be in the form of sheets, but said material may be supplied in the apparatus in the form of'a roll from which sheets of the appropriate length are automatically cut.

it is possible to arrange the edge guides in the processing station so that their spacing can be adjusted to suit various sheet sizes. The proper lateral guidance of the receiving sheet may occur in a favorable way, by inserting into'the chute 12 a sheet guide having lateral edge guides the distance between which corresponds to a particular sheet size.

. We claim:

1. Processing apparatus for use in the production of images according to the silver complex diffusion transfer process, which comprises:

a. a tray for holding a body of processing liquid with edge guide means therein for defining for a radiation-sensitive sheet and for a receiving sheet two separate and vertically spaced paths through the tray which are curved in the longitudinal direction and converge towards each other in the direction of sheet movement,

. separate pairs of feed rollers adjacent the inlet of the respective paths for advancing said sheets separately towards said edge guide means,

. a sloping guide disposed in advance of at least one feed roller pair which leads downwardly to the nip of said roller pair,

. means for feeding a sheet to be gripped by said rollers towards the guide along apath extending at an acute angle relative thereto,

. flexible spring fingers mounted at the side of the sheet path which is remote from the guide and having lower end portions intercepting the free path of the sheet towards the nip of the rollers, the flexibility of said fingers being such that they are set into vibration as they are struck by the leading portion of an advancing sheet,

f. a pair of outlet rollers receiving the sheets from the outlet of the paths for pressing the sheets together and for removing them from the tray, and

g. driving means for rotating said rollers pairs.

2. Processing apparatus for use in the production of images according to the silver complex diffusion transfer process, which comprises:

a. a tray for holding a body of processing liquid with edge guide means therein for defining for a radiation-sensitive sheet and for a receiving sheet two llw separate and vertically spaced pathsthrough the tray which are curved in the longitudinal direction and converge towards each other in the direction of sheet movement,

b. separate pairs of feed rollers adjacent the inlet of the respective paths for advancing said sheets separately towards said edge guide means,

c. a pair of outlet rollers receiving the sheets from the outlet of the paths for pressing of the sheets together and for removing them from the tray,

d. driving means for rotating said roller pairs, and

e. control means controlling said driving means including timing means for regulating the relative rotation of the feed roller pairs for the respective sheet paths so that the leading edge of the sheet moving through said upper path precedes by a sheet at a determined locus for actuating said delay means.

IF I l 

1. Processing apparatus for use in the production of images according to the silver complex diffusion transfer process, which comprises: a. a tray for holding a body of processing liquid with edge guide means therein for defining for a radiation-sensitive sheet and for a receiving sheet two separate and vertically spaced paths through the tray which are curved in the longitudinal direction and converge towards each other in the direction of sheet movement, b. separate pairs of feed rollers adjacent the inlet of the respective paths for advancing said sheets separately towards said edge guide means, c. a sloping guide disposed in advance of at least one feed roller pair which leads downwardly to the nip of said roller pair, d. means for feeding a sheet to be gripped by said rollers towards the guide along a path extending at an acute angle relative thereto, e. flexible spring fingers mounted at the side of the sheet path which is remote from the guide and having lower end portions intercepting the free path of the sheet towards the nip of the rollers, the flexibility of said fingers being such that they are set into vibration as they are struck by the leading portion of an advancing sheet, f. a pair of outlet rollers receiving the sheets from the outlet of the paths for pressing the sheets together and for removing them from the tray, and g. driving means for rotating said rollers pairs.
 2. Processing apparatus for use in the production of images according to the silver complex diffusion transfer process, which comprises: a. a tray for holding a body of processing liquid with edge guide means therein for defining for a radiation-sensitive sheet and for a receiving sheet two separate and vertically spaced paths through the tray which are curved in the longitudinal direction and converge towards each other in the direction of sheet movement, b. separate pairs of feed rollers adjacent the inlet of the respective paths for advancing said sheets separately towards said edge guide means, c. a pair of outlet rollers receiving the sheets from the outlet of the paths for pressing of the sheets together and for removing them from the tray, d. driving means for rotating said roller pairs, and e. control means controlling said driving means including timing means for regulating the relative rotation of the feed roller pairs for the respective sheet paths so that the leading edge of the sheet moving through said upper path precedes by a predetermined short distance the leading edge of the other sheet when the two sheEts come into contact, said control means including means responsive to the introduction of a sheet in proximity to the feed roller pair for the receiving sheet for initiating rotation of said roller pair, means for arresting the rotation of such roller pair after the receiving sheet has been gripped by said roller pair, delay means effective upon actuation for restarting the rotation of said rollers after the elapse of a predetermined time period, and means responsive to the arrival of the radiation-sensitive sheet at a determined locus for actuating said delay means. 